1. Field of the Invention
The present invention relates to gauging devices, and more particularly to devices for measuring the change in the freeboard of a barge with a varying amount of cargo.
2. General Discussion of the Background
The pressing need to accurately measure the amount of cargo on barges and ships have compelled an exhaustive search by the American Shipping Industry to find the best cargo measurement method, thereby improving maritime infrastructure.
The prior art measurement devices of static scales and belt scales are highly inefficient and inaccurate. For example, static scales weigh cargo with at best, 0.2% error, without accounting for human error. Such scales are used as public weighing devices, for example, at truck weighing stations. Belt scales have also proven highly inaccurate in the measurement of bulk-like material, such as coal. For belt scale measurement, an accurate and truly representative sample must be obtained, which of course, poses much difficulty as shown by the 2-3% error in using this method.
Although the prior art does disclose an apparatus for measuring freeboard (U.S. Pat. No. 3,396,470--"Wood"), such device allows freeboard measurements only where a slight surface chop on the water exists. Wood, as designed, will not work properly under conditions of deep swells extending two to three feet below the surface of the tube extending from the bottom of the prior art sounding devices which are not sufficient in length or flexibility to prevent a surge into the sounding tube as swells occur. In the typical prior art device such as Wood, the length and rigidity of Woods tube will prevent the device from working properly in a strong current as it will be swept downstream, preventing sufficient immersion for accurate readings.
To overcome the deficiencies in the prior art devices, the object of the applicant's invention is to provide a device and method for measuring the change in freeboard of a barge or the like, indicating a varying amount of cargo in both still and torrential waters where currents may otherwise sweep prior art devices, preventing accurate freeboard readings.
It is a further object of the applicant's invention to provide a device and method for accurate freeboard readings when barges or the like are tied close together without damaging the device and to allow night readings when glare from flash light would otherwise have obstructed the view of the water.